A tire is installed on a vehicle wheel to provide traction between the vehicle and the road as well as a flexible cushion to absorb shock. Most tires are pneumatic inflatable structures, comprising a doughnut-shaped body of cords and wires encased in rubber and generally filled with compressed air to form an inflatable cushion.
Due to a tire's construction, a tire may act as a spring and store potential energy when the wheel is turned. This spring-like effect is caused by the friction of the road surface which resists turning of the portion of the tire adjacent a contact patch of the tire with the road. As the wheel is turned, portions of the tire near the wheel turn with the wheel while portions of the tire near the contact patch with the ground may resist the turning motion. As a result, a portion of the tire between the wheel and the contact patch may elastically deform. The elastic deformation of the tire, or more specifically the desire of the tire to return to a non-deformed shape, provides the potential energy referred to as tire windup.
Automatic parking (autopark), also known as Active Park Assist, is an autonomous vehicle maneuvering system that moves a vehicle into (park-in) or out of (park-out) a parking spot. Parking spots may range from parallel, perpendicular or angled parking spots. The autopark system aims to enhance the comfort and safety of driving in constrained environments where much attention and experience is required to steer the car. The parking maneuver is achieved by means of coordinated control of the steering angle and speed which takes into account the actual situation in the environment to ensure collision-free motion within the available space.
Tire windup may be more pronounced when tires are turned on a vehicle when it is moving slowly, or not moving at all, such as when the vehicle is performing an autopark event. During, or at the completion of, an autopark event the windup of the tire may cause the steering wheel angle to snap to a different angle when the power-steering motor ceases to provide torque to the steering system. This may also be referred to as steering wheel jerk. An autopark event may be stopped by an operator grabbing the steering wheel, and if the tire has windup when the power-steering motor releases torque to the steering system, the steering wheel may undesirably snap to a new angle in the hands of the operator.